1. Field of the Invention
This invention relates to elastomeric copolyetheresters based on poly(1,4-cyclohexanedimethylene 1,4-cyclohexanedicarboxylate) modified with polypropyleneether glycol which may be extrusion blown into clear flexible bottles or film. The ability to be blow molded is the result of high melt strength.
A polymer having melt strength is described as one which can support its own weight in the molten state after being extruded from a die. When a polymer without melt strength is melt extruded downward from a die, the melt rapidly drops and forms a thin string or breaks. Such polymers are not useful for extrusion blow molding objects. When polymers have sufficient melt strength they can be extruded downward in the shape of a hollow cylinder. Bottles can be blown by clamping a bottle mold around the molten hollow cylinder into which air is blown to form the bottle.
2. Description of the Prior Art
Copolyetheresters known in the art include poly(1,4-cyclohexanedimethylene 1,4-cyclohexanedicarboxylate) modified with polypropyleneether glycol and having an inherent viscosity up to about 0.9. Such copolyetheresters having an inherent viscosity of from 1.0 to about 2.5 have surprisingly been found to have a melt strength higher than would have been expected. For example, polytetramethyleneether glycol would normally be the ether glycol of choice because of easier preparation and better heat stability, but is found to produce a polymer having a significantly lower melt strength than polypropyleneether glycol, thus hindering its ability to be blow-molded.
As stated above, poly(1,4-cyclohexanedimethylene 1,4-cyclohexanedicarboxylate) having an inherent viscosity of less than about 0.9 is known. Poly(1,4-cyclohexanedimethylene 1,4-cyclohexanedicarboxylate) having an inherent viscosity of from 1.0 to about 2.5, however, has a melt strength sufficiently higher to be extrusion blown into useful articles such as bottles or film.